In the context of the present disclosure:
an intrusive aircraft should be understood to be an aircraft not forming part of the formation and risking entering into collision with at least one aircraft of the formation, if no avoidance maneuver is implemented; and
a formation flight is considered to comprise at least two aircraft, notably transport airplanes, namely a followed aircraft, called lead aircraft, and one or more following aircraft. The following aircraft fly by following the aircraft that they follow directly (namely the lead aircraft or another following aircraft) so as to maintain a constant spacing between them.
In a preferred application, in particular in cruising flight, the aircraft fly one behind the other at the same flight level, with the same heading and with the same speed. It is also possible to provide for speed control commands to be applied to the following aircraft such that they make it possible for the following aircraft to have the same position, the same speed, and the same acceleration as the followed aircraft had, in given prior periods.
Such a formation flight offers advantages particularly in terms of fuel consumption. In effect, the formation is generally defined, notably in terms of separation distance, such that a following aircraft is not disturbed by the vortexes created by the aircraft, in particular the lead aircraft preceding it in the formation.
Now, during such a formation flight, an aircraft external to the formation may happen to converge toward at least one of the aircraft of the formation so as to create a risk of collision necessitating the implementation of a separation maneuver.
Airliners are equipped with anti-collision systems of TCAS (Traffic Collision Avoidance Systems) type which make it possible to ensure air traffic safety by preventing the risks of in-flight collision. Thus, when two aircraft converge toward one another, their anti-collision systems compute an estimation of the collision time and transmit an alert informing the crews of each aircraft of a possible future collision: such an alert is generally called “traffic alert” or “TA alert”. If necessary, the anti-collision systems also transmit, for the attention of the crew, a command for an avoidance maneuver in the vertical plane in order to exit from the situation of possibility of collision: such an avoidance maneuver command is generally called “resolution alert” or “RA alert”. The TA and RA alerts are embodied by voice messages and by the display of information in the cockpits.
Such a separation maneuver generally consists in or comprises or comprises implementing a vertical separation between the aircraft concerned, generally of 700 feet for airliners.
Now, such a maneuver generating a modification of altitude of at least one of the aircraft of the formation will break the formation, such that the aircraft can no longer benefit from the above-mentioned advantages of the formation flight in such a situation.
Such standard management of the formation flight upon a risk of collision is not therefore satisfactory.